Semiconductor large-scale integrated circuits are required to have a higher density for improving the integration density and achieving high performance. In the wake of miniaturization of wiring patterns, it has been required to reduce the process line width and to shift to multilayer wiring in order to cope with the densification. Such multilayer wiring structures are formed by repeating several deposition and etching of a conductive film and an insulation film, and differences in level on the surface tend to be larger thereby. On the other hand, focal depth of resists used for patterning of wiring tends to be shallow in the wake of miniaturization of wiring patterns. Accordingly, patterning is more largely influenced by the differences in level on the surface, which is regarded as a problem. Therefore, wide-area flattening is required to get rid of the differences in level on the surface in order to perform patterning easily.
As such a wide-area flattening technology, coating technology with a resin such as polyimide, etch back technology on metal and an insulation film, reflow technology on metal and an insulation film, and chemical mechanical polishing (CMP) technology are known.
The chemical mechanical polishing (CMP) step is performed by supplying slurry which contains polishing particles onto a substrate and by using a polishing pad attached to a polishing apparatus. In this case, the polishing particles polish the surface mechanically under pressure from the polishing apparatus, and chemical ingredients contained in the slurry chemically react to the surface of the substrate to remove the surface part of the substrate chemically.
As a rule, various kinds of slurry are used for chemical mechanical polishing (CMP) depending on the type of a film to be removed and a property thereof. The polishing particles to be used include silica (SiO2), ceria (CeO2), alumina (Al2O3), titania (TiO2), zirconia (ZrO2), etc., and can be used selectively depending on a film to be polished.
Previously, it has been generally investigated the use of silica-based slurry as a slurry for chemical mechanical polishing (CMP) to flatten an insulation film such as a silicon oxide film. The silica-based slurry is produced by grain growth of silica particles through thermal decomposition of silicon tetrachloride, and by pH adjustment with the use of an alkaline metal-free alkaline solution such as ammonia.
As a slurry for chemical mechanical polishing (CMP) of an inorganic insulation film such as a silicon oxide film, ceria slurry which contains ceria particles as polishing particles have been used. Ceria particles have lower hardness compared to silica particles or alumina particles, and are hard to generate defects such as scratches on the surface of a polished film, thereby being considered to be useful. Ceria particle are known as a strong oxidizing agent and have a chemically active property. Accordingly, ceria slurry is considered to be useful for application to chemical mechanical polishing (CMP) of an inorganic insulation film such as a silicon oxide film (e.g., see Patent Document 1, Patent Document 2).
In a conventional step for forming STI (Shallow Trench Isolation), a polishing step is performed with the use of a silicon nitride film as a hard mask. The silicon nitride film is formed on a substrate, and then a trench is formed on a prescribed area of the silicon nitride film and the substrate. A silicon oxide film is formed so as to fill the trench, and then the silicon oxide film is polished to form a device isolation film on the trench part. In this case, the silicon oxide film is polished until the silicon nitride film is exposed by using dry ceria slurry, etc., which can secure high polishing selectivity between a silicon oxide film and a silicon nitride film.
On the other hand, a polysilicon film is used as a polishing stop film in some cases instead of using a silicon nitride film as a hard mask. In this case, since polysilicon films have lower hardness compared to silicon nitride films, there arises a problem that defects such as scratches are tend to generate on the surface of the polysilicon film after CMP polishing. When the surface after CMP polishing has a defect such as a scratch, snapping failure and short circuit failure can be occurred in minute transistors and wiring.
In order to suppress defects such as scratches, it is possible to apply wet ceria, for example, to the CMP step as abrasive grains. This is because wet ceria has a polyhedron structure, and can largely improve scratch defects thereby.
Although defects such as scratches can be remedied by the use of wet ceria, polishing selectivity between a silicon oxide film and a polysilicon film is not sufficient. Then, chemical mechanical polishing (CMP) involves a problem that a polysilicon film of a polishing stop film is polished excessively. Accordingly, it has been required to improve the CMP polishing agent.
For example, Patent Document 3 discloses a polishing agent which contains polyoxyethylene amine ether as a polish finisher for polishing a polysilicon film. Patent Document 4 discloses a polishing agent which contains a cationized polyvinyl alcohol, and at least one type of saccharide selected from the group consisting of an amino sugar, a derivative thereof, a polysaccharide containing an amino sugar, and a derivative thereof. These polishing agents, however, do not have a sufficient protective function for a polysilicon film, and have a problem of cleaning property after CMP polishing. Accordingly, it has been required for improving a CMP polishing agent.